The present invention relates to solar refrigeration systems.
Energy produced by cheap fuels, on which a civilized society of today is based, are most likely to start to run out. Thus, methods of and apparatuses for directly using limitless solar energy are attracting our attention. A considerably large portion of a total of consumption of energy for public's livelihood consists of energy consumption for air conditioning and that for freezing of perishable foods. Apparently, if solar energy can be used for producing a low temperature, the energy we need for air conditioning and freezing, which is currently given by fossil fuels such as an oil, will be partly or wholly replaced by solar energy and the fossil fuels can be conserved. To accomplish this, a system in which a steam generated by solar heat is used to operate a steam engine that drives a compressor and another system in which a hot water heated by solar radiation is used to operate an absorption refrigeration system have been devised. In the latter case, problems encountered in practical applications were solved with the existing techniques.
A conventional absorption refrigeration system with solar energy employing a solar collector-refrigerant gas generator is disclosed on page 43 of "Refrigeration and Air Conditioning June 1977" and will be explained hereinafter in connection with FIG. 1.
In FIG. 1, the reference numeral 1 denotes a solar collector which serves as a refrigerant gas generator also. The reference numeral 2 denotes a top header or a vapor liquid separator in which vapor and liquid are separated; the reference numeral 3 denotes a condenser; the reference numeral 4 denotes an expansion valve; the reference numeral 5 denotes an evaporator; the reference numeral 6 denotes a refrigerant gas absorber; the reference numeral 7 denotes a pump; the reference numeral 8 a heat exchanger; the reference numeral 9 denotes a conduit for refrigerant gas; and the reference numeral 10 a conduit for a weak solution containing a low concentration of refrigerant gas. This system operates as follows: rich solution containing a high concentration of refrigerant gas dissolved therein flows into the solar collector-generator 1 from its lower end and the rich or concentrated solution is heated with solar radiation high enough as to release the refrigerant vapor, thus becoming the weak spent or dilute solution. In the top header 2 connected to the upper end of the solar collector-generator 1, the vapor gas is separated from the liquid. The refrigerant gas flows from the top header 2 to the condenser 3 through the conduit 9 for condensation. The condenser 3 is cooled with cooling water or air. The thus formed liquid refrigerant expands in the expansion valve 4 from the high-pressure level in the condenser 3 to the low-pressure level in the evaporator 5. In the evaporator 5 the liquid refrigerant boils at low temperature to produce cooling. The gaseous refrigerant flows from the evaporator 5 to the absorber 6. The weak solution separated from the refrigerant vapor in the top header 2 flows through the conduit 10 into the heat exchanger 8 where it gives heat to the relatively low temperature rich solution passing through the heat exchanger 8. The thus cooled weak solution flows from the heat exchanger 8 into the absorber 6 where it absorbs the refrigerant gas to become the rich solution. Because the absorber 6 is cooled with cooling water or air, the temperature of the rich solution is as low as that of the cooling water or air. Because the pressure of the rich solution in the absorber 6 is lower than the pressure thereof in the collector 1, the pump 7 is provided to pump the rich solution toward the collector 1.
The thermal efficiency of such an absorption refrigeration system as previously described largely depends on the efficiency of heat exchange between the rich solution and the weak solution. Thus to increase the thermal efficiency of the system the temperature of the rich solution as it enters the solar collector 1 must be raised with the heat exchange process between the rich solution and the weak solution. For this it is necessary to eliminate heat losses by thermally insulating the top header 2, the conduit 10 between the top header 2 and the heat exchanger 8, and the heat exchanger 8 per se in addition to increasing the effective area through which the heat is transferred in the heat exchanger 8. This part of the cycle is the highest in temperature and thus the heat is most likely to be lost. As described above, the conventional refrigeration system shown in FIG. 1 has a shortcoming that the thermal efficiency is not high enough.